There exists currently a range of technologies for controlled release of substances from particles. These are used in a wide range of applications, from human therapeutics to industrial applications. The majority of these technologies have been directed to achieving slow, relatively constant release of an encapsulated substance. This is commonly of use therapeutically to provide a continuous effective dose of a drug and avoid large variations in concentration of the drug in bodily fluids. However certain applications require instead that an encapsulated species be released in a sudden burst on exposure to a triggering stimulus. Such applications additionally require that the encapsulated species be retained in the particles, prior to the triggering stimulus. Commonly such “triggered” release is required when encapsulation of the species in the particles provides some protection from a harsh environment.
One example of such an application is laundry detergents. Enzymes are highly desirable components of laundry detergents because of their ability to break down a range of commonly occurring stains on clothing and other fabric items (e.g. towels, table cloths, bed sheets etc). Suitable enzymes include proteases, lipases, cellulases and amylases. Liquid detergents present a challenging environment to enzymes due to their relatively high pH (about 8-9), presence of other enzymes (e.g. proteases), and detergent components such as surfactants, preservatives, and bleaches. A range of additives are commonly added in order to stabilise enzymes in the detergent formulations. Nevertheless, some enzymes, notably proteases, remain notoriously difficult to stabilise for the long shelf life required (up to 2 years).
A potential method for stabilising enzymes in liquid laundry detergents is to encapsulate them in a protective matrix which enables rapid release when added to a wash. WO2006/066317 (the contents of which are incorporated herein by cross reference) describes encapsulation of biological materials such as enzymes in silica particles for controlled release. Silica particles present an interesting option for encapsulation of laundry enzymes, as they are not dissimilar to materials already added as softening agents to laundry detergents (e.g. zeolites, silicates and citrates) in relatively high proportions (up to about 10%). Silica particles are also expected to be stable at pH about 9.0. (On increasing the pH from 9 to 10.7, there is an increase in the solubility of amorphous silica due to the formation of silicate ions in addition to monosilicic acid. Above pH=10.7, silica dissolves to form soluble silicate.)
There is a need to achieve an effective ‘triggered release’ of enzyme from the particles on addition of the detergent to the wash. If such a method could be achieved, the technology may also be extendable to other applications in which rapid release of a species encapsulated in particles is desired in activation by a suitable “trigger”.